To the extent characteristics of a drive are identified in this description of the invention, they also apply to a pump, in particular to an artificial heart and vice versa.
For example, such a pump can replace the heart intracorporal as artificial heart and thus save the life of patients who have heart disease and who have previously been primarily dependent on a donor heart. Thereby, in contrast to other, previously routinely used systems, the quality of life of the patient remains preserved to a great extent.
Heart-assist systems are generally known in the prior art. A number of heart-assist systems have already been developed since the 20's and are being used in humans with increasing success. Here, a distinction is generally made between systems that assist the heart and systems that replace the heart.
When using systems that assist the heart, the heart is limited in its functionality, but can however continue to still fulfill a part of its original pumping capacity. One of the two heart chambers is connected in parallel or in series to an artificial pump that assists the heart. Under certain circumstances, a recovery of the heart can thereby be achieved and the system can then be removed.
If the natural heart is weakened so severely that assisting the heart is not enough to sufficiently supply the body with blood, and a recovery of the heart is not to be expected, the natural heart must be removed and be replaced with an alternative, for example, an artificial heart or a transplanted donor heart.
As, however, the demand for donor hearts continues to increase and simultaneously, the willingness to donate is falling, an adequate number of donor hearts is no longer available. The use of an artificial heart can reduce the high death rate of patients on the waiting list.
Systems made by Incor assist the heart and that are already used in humans. Those made by Cardiowest are used, for example, heart replacements. The individual systems assisting or replacing the heart are significantly different in their design and operation. The systems can be divided into continuously operating radial pumps or axial pumps (e.g. Incor) and pulsing reciprocating and rotary pumps (e.g. Cardiowest).
Force transmission between the drive and a pump membrane is performed by rigid mechanical connections (e.g. Abiocor 2) hydraulically (e.g. Abiocor 1), pneumatically (e.g. Cardiowest) or magnetically (e.g. Magscrew). Thereby, the transmission of force takes place in the form of a thrust or a rotational moment, either directly (e.g. Cardiowest) or through a stepdown transmission (e.g. Abiocor 2).
Particular attention is being paid to heat lost by the drive, which can damage the blood by coagulating it. By partially or completely filling the drive with cooling fluid that also serves as lubricant for storage in several concepts such as, for example, as in U.S. Pat. No. 5,300,111, an attempt is being made to dissipate heat from the blood and the surrounding tissue as homogeneously as possible.
The bearings of the pumps, conventional ball bearings and floating bearings (e.g. Abiocor 2), suffer wear or in the case of hydrodynamic bearings, e.g. as in U.S. Pat. No. 5,360,445 and magnet bearings, are largely wear-free. The trend is in the direction of low-wear drives that have a service life of at least 5 years. For a mechanical release of the bearings, rotation-symmetric drives are used in which the forces of attraction compensate as the result of centering between the stator and the rotor in rotating machines or the primary part and the secondary part in linear drives. Thus, the bearings are lighter and more compact and have longer service lives. As an ideal centering cannot be implemented technically, forces of attraction are created in all previous systems between stator and rotor or the primary part and secondary part that lead to premature wear of the bearings.
Most of what is common between the invention and prior art can be found in the electric linear drives without transmission, for example in U.S. Pat. No. 5,360,445 and U.S. Pat. No. 5,300,111.
Only when the movable parts or the fixed parts are ideally centered is a resulting force radially absent in any of the previous concepts mentioned above.
As ferromagnetic material is always used in one part and magnetic material in the other part, forces of attraction are always created between the two parts that compensate each other out only when concentric. As an ideal centering cannot be done technically, there are always more or less pronounced radial forces between the two parts. In addition to the actual guiding function, they load the bearings and lead to increased wear of the bearings, as a result of which the service life is reduced.
Previous concepts do not maximize the density of power. As described in the Panton patent (U.S. Pat. No. 5,300,111), in the development of artificial hearts the transmission of heat to the surrounding tissue and the blood can be realized by using suitable cooling steps. Rather, the weight and the dimensions of the artificial heart are the main problem of the artificial heart because of the severely limited space in the chest cavity at a specified propelling thrust. Although according to the concept of passing current as described in Goldowsky's patent (U.S. Pat. No. 5,924,975) by selecting equally long coils and magnet segments with minimum ohmic loss, the force is maximized, but the force continues to significantly fluctuate as previously described depending on the overlap relationship and does not take on the absolute maximum value.
The reason for this is an enlargement of the magnetic field (leakage) in the sections of the adjacent coils that are not supplied with current. Thus, for ensuring a specified power, the actuation system must be configured larger than a system which would also utilize leakage flux.
The concept as in Yeakley (U.S. Pat. No. 6,194,796) uses this leakage flux by utilizing only one coil, but this long coil leads to high ohmic losses, significantly reducing the degree of effectiveness.
The magnetic flux density inside coils in all concepts is at a maximum as large as the flux density created by the magnet.
According to Lorentz, the force upon the coil through which current flows is proportional to the magnetic flux density. As a result of an increase of the magnetic flux density, for example, in the form of a flux concentrator, the force could thus be significantly increased at constant ohmic power dissipation. Thereby, an increase in the degree of effectiveness would be possible or the drive could be made smaller.
Rotary drive concepts only create a continuous speed of the flow of the blood, so that the pump behavior of the human heart it is not recreated. Likewise, in these concepts, the high speeds of rotation of the rotors are a disadvantage, in that high shear forces are exerted upon the blood that lead to increased damage of the blood.
Concepts as in Vitale (U.S. Pat. No. 6,190,409 B1) are in a position to recreate the pumping process of the human heart in its pumping capacity, however, as the result of the revolving motor within the pump, the course of the pressure stream and volume stream of the blood cannot be sufficiently recreated as in the human heart. Further, these systems sometimes work with an increased beat rate.
In the Abiocor, silicon oil is used that fills the entire drive. As no compressible medium (e.g. air) is present in the system, the membrane is actively aspirated in the diastolic phase (filling phase), as a result of which a hemodynamically unfavorable collapse of the atrium can occur.
To ensure a certain quality of life and perspective for the patient, organ-assisting or organ-replacing systems must be as quiet as possible and have a guaranteed service life of five years. All previous concepts use power converters such as mechanical, magnetic or pneumatic transmissions. The many movable parts create, however, a higher level of noise and increased wear.